Edit1:I narrowed the problem down to the wz5100 functions. As soon as one of Ethernetserver or Ethernetclient is used, the arduino stops working. If I only use Ethernet.begin(mac, ip) I can at least ping the arduino.

Edit2:Problem seems to be the toolchain on my amd64 linux box. On my windows machine everythings ok now. This is sad. I tried avr-gcc-4.5.3 and avr-gcc-4.3.6 both without success.

Does anybody know which combination of avr-gcc / avr-libc is working on amd64 linux ?

Hi,I changed those lines but unfortunately it doesn't help. I also tried the "blink" example this morning and found out it doesn't work on linux, too.Can you post me your toolchain versions (avr-gcc, avr-libc) ?

I was facing a similar problem here, but I am using a 32 bits workstation. To fix the issue I followed the steps of Reply #5 but it wasn't enough, so I have updated all the Ethernet utilities sources [1] and now it is working. I will do more tests but looks like it is fixed for me. I hope it can help you too.

Have you tried it with or without DHCP? I am still unable to connect to the internet using static IP, but I can connect to the internet with DHCP. I can ping the Arduino interface using both modes but can't access the internet with an static IP. I have tried passing the gateway and the subnet too, without success.